1. Field of the Invention
This invention relates to a fuel injection system for internal combustion spark ignited engines and more particularly to a system incorporating means for controlling the volume of fuel provided to the engine as a function of the engine operating parameters and for varying the volume of fuel as a function of fuel temperature adjacent to the injectors to maintain the weight of fuel provided independent of fuel temperature variation.
2. Prior Art
Fuel control systems which measure engine operating parameters and inject a metered quantity of fuel into the engine cylinders, in timed relation to the engine operation, as a function of the parameters, provide better control over the fuel-air ratio in the engine cylinders than the more conventional carburetor systems. Since this precise control of the fuel-air ratio can improve the engine's efficiency and decrease the quantity of pollutants in the engine3 s exhaust, the interest in these systems has increased in direct proportion to the cost of fuel and the tightening of government regulations limiting the permissible quantities of undesirable emissions in vehicle exhausts.
Within the engine combustion chambers, the air and fuel react with one another on a weight basis so that it is important to control the weight of fuel provided to the engine rather than its volume; but prior art fuel metering injectors are typically volume measuring devices. A common form of injector consists of a normally closed valve which is opened for a period of time controlled by the engine operating parameters. The pressure to the injector is maintained constant so that a controlled volume of fuel is passed by the injector during the period of time that it opened.
The error in fuel-air ratio that results from controlling the volume of the fuel, rather than its weight, may be considerable since fuel density varies substantially as a function of fuel temperature. A typical gasoline mixture may change in density by about 1% for each temperature change of 10.degree. F. The fuel temperature at the injector may vary from about -20.degree. F during a cold start to about 250.degree. F in a system where the injector is disposed adjacent to the engine intake valve, during warmed up engine operation. The injector temperature stabilizes well below the engine intake valve temperature because of the cooling effect of the fuel. Thus, a substantial fuel density variation will occur and a fuel system which only monitors furl volume may provide a substantially erroneous fuel-air ratio.